Osny Oliveira Santos Bacchi

Management effects on nitrogen recovery in a sugarcane crop grown in Brazil

The present studys objectives were to quantify the fertilizer-N and residue-N balances of a sugar cane crop under two trash management systems. The fate of nitrogen (N) derived from fertilizer (NdfF) and N derived from residue (NdfR) was studied comparing: (i) the traditional harvest system with trash burning before harvest (“trash burning”) and (ii) an alternative system without trash burning, in which crop residues are left on the soil surface (“trash mulching”). The experiment consisted of three treatments: (i) T1: at planting, the sugarcane crop was fertilized with 63 kg N ha−1 as 15N-labeled ammonium sulfate, and after the 1st harvest received unlabeled trash from T2; (ii) T2: at planting, the crop was fertilized with 63 kg N ha−1 as unlabeled ammonium sulfate. At the 1st harvest time, this treatment received the labeled trash from T1; (iii) T3: at planting, the crop was fertilized with 63 kg N ha−1 as 15N-labeled ammonium sulfate, and every year, immediately before cutting, the crop residues were burnt. After the first harvest fertilizer-N was applied over the total soil area at a rate of 80 kg N ha−1 as unlabeled ammonium sulfate. The results indicated that the trash remaining as a surface blanket resulted in an average N recycling of 105.0 kg ha−1 year−1, while the practice of burning the trash produced an average N loss from the system of 83.5 kg ha−1 year−1. At the first harvest, about 75% of the labeled N was recovered in the soil–plant system. The majority was found in the plant, indicating a high availability of the fertilizer-N for the crop. At the end of the third crop cycle (2nd ratoon crop harvest), the total output of fertilizer-N (export+burning) was 60% for the burnt-trash treatment, and only 42% (export) for the trash-blanket treatment. The N liberated from the residue is mainly immobilized in the soil, reflecting that sugarcane trash is an N source of slow availability to the crop. This study indicated that green cane harvesting followed by mulching leads to a more efficient recycling of the N applied to the system and therefore reducing fertilizer-N needs.

Software to model soil water retention curves (SWRC, version 2.00)

A software for the adjustment of soil water retention curves (SWRC) is presented, using twelve models found in the literature.

Variability of soil water content and bulk density in a sugarcane field

The change in management practices of the sugarcane crop in Brazil, from the traditional trash burning before harvest to the new practice that leaves harvest residues on the field after harvest, can lead to alterations in the water regime and also in soil compaction levels. In this study a neutron-gamma surface gauge was used to monitor spatial and temporal variabilities of soil moisture and density in a experimental sugarcane area submitted to 3 harvest management practices: (i) mulched crop with harvest residues, (ii) crop with bare inter-row, and (iii) crop with ash residues from trash burning before harvest. Variability of soil water content and bulk density was studied using geostatistical tools and analysis of variance was used to compare averages. Autocorrelations and semivariograms indicate a spatial dependence of soil water contents, which were higher in the presence of trash residues left on the soil surface after harvest. The average difference between treatments (i) and (ii) was about of 15%, indicating the beneficial mulching effect with respect to soil water retention. Differences between (ii) and (iii) were much smaller.

STATE-SPACE APPROACH FOR THE ANALYSIS OF SOIL WATER CONTENT AND TEMPERATURE IN A SUGARCANE CROP

The state-space approach is used to describe surface soil water content and temperature behaviour, in a field experiment in which sugarcane is submitted to different management practices. The treatments consisted of harvest trash mulching, bare soil, and burned trash, all three in a ratoon crop, after first cane harvest. One transect of 84 points was sampled, meter by meter, covering all treatments and borders. The state-space approach is described in detail and the results show that soil water contents measured along the transect could successfully be estimated from water content and temperature observations made at the first neighbour.

Field spatial and temporal patterns of soil water content and bulk density changes

Umidade (q) e densidade do solo (rs) influenciam importantes processos no solo e planta tais como: movimento de agua, compactacao do solo, aeracao do solo e desenvolvimento radicular. Baseado neste fato, questoes referentes a variabilidade espacial e temporal de q e rs para diferentes periodos do ano e diferentes fases de desenvolvimento da cultura do cafe tornam-se de extremo interesse. Este trabalho teve como objetivo caracterizar padroes espaciais e temporais de q e rs durante diferentes periodos do ano e verificar se existem mudancas temporais significativas de rs na superficie do solo quando submetida a ciclos de umedecimento/secagem. O experimento foi conduzido em campo cultivado com cafe em um solo classificado como Nitossolo Vermelho Eutrofico. O experimento iniciou-se em maio de 2001 com espacamento de 1,75 m entre linhas e 0,75 m entre plantas. Medidas de q e rs foram feitas metro a metro ao longo de 200 m usando uma sonda de superficie neutron/gama. Durante o periodo umido nao houve padroes de diferenca espacial para q, enquanto que para o periodo seco o contrario foi observado. Estes padroes podem ser associados a eventos de precipitacao alterando a estrutura de correlacao espacial para observacoes adjacentes de q. Para rs existem mudancas temporais na superficie do solo ao longo do periodo estudado como uma consequencia dos ciclos de umedecimento/secagem no campo.

Principles of crop modeling and simulation: I. uses of mathematical models in agricultural science

A tecnica de modelagem em agricultura pode ser util para definir as prioridades de pesquisa, bem como para melhor entender as interacoes que ocorrem no sistema solo-planta-atmosfera. O modelo pode ser utilizado para estimar a importância e o efeito de certos parâmetros no intuito de definir os fatores a serem considerados. O modelador deve definir seus objetivos antes de iniciar o trabalho experimental, bem como desenvolver um modelo que atenda o objetivo proposto.

Soil bulk density evaluation by conventional and nuclear methods

Among the methods used to measure soil bulk density, the following have been prominent: paraffin sealed clod (PS), volumetric ring (VR), and the modern methods like gamma ray computed tomography (GCT) and the neutron/gamma surface gauge (SG). The objective of this work was to compare soil bulk density values obtained through these methods, with the aim of assisting researchers on the choice of the more appropriate method. For this, a 200-m spatial transect was chosen in an experimental area cultivated with coffee, belonging to ESALQ/USP, Piracicaba, SP, Brazil. The SG readings were first taken in the field and thereafter soil samples were collected at 8 different points, spaced at 25 m, for the other methods. The lowest values of soil bulk density were obtained for the SG method (average 1.468 g/cm3) and the highest for the PS (average 1.685 g/cm3), which was similar to the GCT method (average 1.684 g/cm3). The average soil bulk density for the VR method, which has been used in soil science as a standard method, was 1.544 g/cm3. The Tukey test indicates that the PS and GCT methods do not differ significantly (P > 0.05). They do differ in comparison with VR and SG, which also do not differ among themselves.

Hydraulic variability in space and time in a dark red latosol of the tropics

Abstract Detailed information of the variability of soil properties and processes in space and time is presented for a dark red latosol (Alfisol) of the county of Piracicaba, S.P., Brazil. Data were collected on 25 plots along a 125 m transect during the years 1989–1991, and consisted of the soil water content θ in the 0–150 cm soil layer and the water pressure heads h at 135 and 165 cm depths. These raw data were used to characterize variabilities in space and time using classical statistics and in a second step to analyse the difficulties in calculating soil water storage, soil hydraulic conductivities, hydraulic gradients, soil water fluxes and water balances. In general, there was a great variability of hydraulic properties and processes, which is fairly constant in time in the case of basic data like soil water content and potential, but not in the case of calculated data like hydraulic conductivities and gradients, and soil water flux densities. A discussion is presented of the difficulties of using Darcys equation to estimate soil water flux densities due to the exponential K (θ) and K ( h ) relationships of the hydraulic conductivity K , and of the influence of variability in space and time on the establishment of water balance components.

Damage to soil physical properties caused by soil sampler devices as assessed by gamma ray computed tomography

Soil sample physical properties can be greatly affected during soil sampling procedures. Improper procedures can impose modifications on soil sample structure and consequently lead to wrong measurements of soil properties. The objective of this work was to evaluate the damage caused by soil samplers to soil structure through the analysis of computed tomography (CT) images. A first generation tomograph was used, having a 241Am source and a 7.62 × 7.62 cm NaI(Tl) scintillation crystal detector coupled to a photomultiplier tube. Results confirm the effect of soil sampler devices on the structure of soil samples, and that the compaction caused during sampling causes significant alterations to soil bulk density. Through the use of CT it was possible to determine the level of compaction and to make a detailed analysis of the soil bulk density distribution within the soil sample.

Variability of water balance components in a coffee crop in Brazil

Establishing field water balances is difficult and costly, the variability of their components being the major problem to obtain reliable results. This component variability is presented herein for a coffee crop grown in the Southern Hemisphere, on a tropical soil with 10% slope. It was observed that: rainfall has to be measured with an appropriate number of replicates; irrigation can introduce great variability into calculations; evapotranspiration, calculated as a remainder of the water balance equation, has exceedingly high coefficients of variation; the soil water storage component is the major contributor in error propagation calculations to estimate evapotranspiration; and that runoff can be satisfactorily controlled on the 10% slope through crop management practices.